As with any cooking utensil, food thermometers should
be washed with hot soapy water, but most thermometers should
not be immersed in water. Wash carefully by hand. Use
caution when using a food thermometer. Some models have
plastic faces, which can melt if placed too close to
heat or dropped in hot liquid. Thermometer probes are
sharp and should be stored with the probe in the stem
sheath. Some glass thermometers are sensitive to rough
handling and should be stored in their packaging for
extra protection or in a location where they will not
be jostled.

There are two ways to check the accuracy of a food
thermometer. One method uses ice water, the other uses
boiling water. Many food thermometers have a calibration
nut under the dial that can be adjusted. Check the package
for instructions.

Ice Water Method

To use the ice water method, fill a large glass with
finely crushed ice. Add clean tap water to the top of
the ice and stir well. Immerse the food thermometer
stem a minimum of 2 inches into the mixture, touching
neither the sides nor the bottom of the glass. Wait
a minimum of 30 seconds before adjusting. (For ease
in handling, the stem of the food thermometer can be
placed through the clip section of the stem sheath and,
holding the sheath horizontally, lowered into the water.)
Without removing the stem from the ice, hold the adjusting
nut under the head of the thermometer with a suitable
tool and turn the head so the pointer reads 32 °F.

Boiling Water Method

To use the boiling water method, bring a pot of clean
tap water to a full rolling boil. Immerse the stem of
a food thermometer in boiling water a minimum of 2 inches
and wait at least 30 seconds. (For ease in handling,
the stem of the food thermometer can be placed through
the clip section of the stem sheath and, holding the
sheath horizontally, lowered into the boiling water.)
Without removing the stem from the pan, hold the adjusting
nut under the head of the food thermometer with a suitable
tool and turn the head so the thermometer reads 212
°F.

For true accuracy, distilled water must be used and
the atmospheric pressure must be one atmosphere (29.921
inches of mercury). A consumer using tap water in unknown
atmospheric conditions would probably not measure water
boiling at 212 °F. Most likely it would boil at least
2 °F, and perhaps as much as 5 °F, lower. Remember that
water boils at a lower temperature in a high altitude
area. Check with the local Cooperative Extension Service
or Health Department for the exact temperature of boiling
water.

Even if the food thermometer cannot be calibrated,
it should still be checked for accuracy using either
method. Any inaccuracies can be taken into consideration
when using the food thermometer, or the food thermometer
can be replaced. For example, water boils at 212 °F.
If the food thermometer reads 214 °F in boiling water,
it is reading 2 degrees too high. Therefore 2 degrees
must be subtracted from the temperature displayed when
taking a reading in food to find out the true temperature.
In another example, for safety, ground beef patties
must reach 160 °F. If the thermometer is reading 2 degrees
too high, 2 degrees would be added to the desired temperature,
meaning hamburger patties must be cooked to 162 °F.